U.S. Pat. No. 5,386,253 to Fielding, incorporated herein in its entirety by this reference, discusses exemplary projection systems utilizing one or more spatial light modulators (SLMs). As noted in the Fielding patent:                Spatial light modulator devices include so-called “active matrix” devices, comprising an array of light modulating elements, or “light valves,” each of which is controllable by a control signal (usually an electrical signal) to controllably reflect or transmit light in accordance with the control signal A liquid crystal array is one example of an active matrix device; another example is the deformable mirror device (DMD) developed by Texas Instruments . . .See Fielding, col. 1, II. 13–21. Of course, yet other types of light “engines,” or sources, exist, and various of them may be used in connection with the inventions described herein.        
Regardless of the type of light sources and modulators used, audiences frequently desire to see images high in detail and richness and low in objectionable artifacts. High resolution and image quality in particular facilitates suspension of disbelief of an audience as to the reality of the projected images Such quality indeed often is an important factor in the overall success of the motion picture viewing experience among today's audiences.
Producing these high-resolution images is not without added cost, however. Imax Corporation, for example, the intended assignee of this application, utilizes not only specialized cameras and projectors, but also seventy millimeter, fifteen perforation film to increase the resolution and quality of projected images. Conventional electronic projectors (and especially these utilizing SLMs), by contrast generally cannot supply equivalent resolution in projected images. As well such electronic projectors frequently fail to furnish the dynamic range and overall brightness of images provided by large-format films. They nonetheless may desirably (or necessarily) be employed to display non-film-based images such as (but not limited to) computer-generated graphics or material captured with electronic cameras.
U.S. Pat. No. 5,490,009 to Venkateswar, et al., also incorporated herein in its entirety by this reference, details techniques purporting to enhance image resolution in systems employing multiple SLMs. According to the Venkateswar patent, sub-images generated by different SLMs are simultaneously displayed such that some sub-images are spatially offset horizontally or vertically from others. This results in partial superposition of the sub-images, with the offset supposedly allowing a two-SLM system (with each SLM having “x” pixels per row) to provide “a perceived quality approaching that of a system that generates a single image from an SLM having 2(x) pixels per row.” See Venkateswar, col. 2. II. 41–43.
U.S. Pat. No. 5,612,753 to Poradish, et al., additionally incorporated herein in its entirety by this reference, discloses alternative techniques for, purportedly, increasing brightness of projected images or extending the projected number of gray levels. FIG. 1 of the Poradish patent illustrates a projection system in which light from two sources is reflected toward separate lens systems and then focused separately on distinct color wheels. Light from each color wheel thereafter is reflected to an SLM (preferably a DMD) via a total internal reflection (TIR) prism, with each SLM modulating the light and directing it back to the associated TIR prism. As directed, the light is then transmitted by the prisms to lenses for projection onto a screen. See Poradish, col 3, II. 6–39. In essence, therefore, the Poradish patent contemplates use of dual DMDs present in parallel paths existing from separate light sources to a screen.
While the techniques of the Venkateswar and Poradish patents arguably might enhance the resolution of an image produced by a digital projector, alone either is unlikely to provide resolution consistent with that of large-format film. Enhanced resolution of images produced by digital projection systems thus remains a significant issue for those engaged in development of commercial projection equipment. Absent further advancement in this area, viewing of electronically projected images remain less satisfying to public audiences.